The overall objectve of the research program is the description of events during the initial phases of mammalian embryogenesis in cellular and molecular terms. During the proposed project period, the research will be focused primarily on two aspects of preimplantation embryogenesis: (1) A definition of the role of gene products synthesized during oogenesis in the developmental program which follows fertilization; and (2) a definition of the major and significant interactions between the uterine stage embryo and the maternal reproductive tract which permit the completion of those events leading up to implantation. Previous work in this laboratory has provided a background description of gene expression during the preimplantation period of rabbit embryogenesis, in terms both of ribonucleic acid and of protein synthesis. It is anticipated that this description will require refining as work progresses during the proposed project period. Current evidence is consistent with the hypothesis that gene products synthesized during mammalian oogenesis are stable participants in the protein synthesis which follows fertilization. The time of entry of embryonic ribonucleic acids into the protein synthetic apparatus, as well as their nature, remains to be clarified. Embryo-uterine interactions will be explored in the context of the molecular basis of the requirement for synchrony between the developing blastocyst and the hormonally-stimulated reproductive tract, and of the mechanism(s) whereby the reproductive tract induces embryonic diapause. These questions will be explored using the techniques of two-dimensional polyacrylamide gel protein electrophoresis and autoradiography, transmission and high-voltage electron microscopy of embryonic thin and thick sections and DNA spreads, cell fractionation and ultracentrifugation, liquid scintillation counting, and phase and ultraviolet microscopy.